Improve GitHub Codespaces configuration

[chykon]

Description & Motivation

Thanks to contribution tried GitHub Codespaces along with ROHD. Pretty handy for certain situations. I would like to suggest some improvements:

• The initial container configuration uses the Dart (Community) template, which is marked as Deprecated (No longer maintained). It is proposed to replace it with the actual template Ubuntu version 22.04. The default template (Default Linux Universal) is not suitable due to being based on Ubuntu 20.04, which would require compiling Icarus Verilog version 11 and increase container deployment time.
• Because the Ubuntu template is basic and generic, it requires installation of the software needed to work on ROHD. This is done with a setup script autorun by the updateContentCommand when the container is created.
• The public key for the Dart repository is suggested to be stored locally, rather than downloaded each time the container is created.
• When launching the container for VSCode, the Dart extension will be installed. It was in the original configuration as well.

Separately, I would like to ask for opinions: is it necessary to automatically open files when starting codespace? Now the files README.md, CONTRIBUTING.md, CODE_OF_CONDUCT.md are opened. This should help new contributors, but it can also be annoying.

Related Issue(s)

No.

Testing

You can check:

Backwards-compatibility

Is this a breaking change that will not be backwards-compatible? If yes, how so?

No.

Documentation

Does the change require any updates to documentation? If so, where? Are they included?

No, but it will be possible to add the GitHub Codespaces badge to README.md. Instructions here.

[mkorbel1]

Thank you so much @chykon for this PR, this looks great! I was able to open your branch and it all looks good.

I think an "Open in GitHub Codespaces" badge would be a great addition to the README. If you like, you can add it to this PR, otherwise I will include it in another documentation-related PR that I'm working on.

[mkorbel1]

Looks great, thank you for your contribution!

@chykon, we really appreciate all the thought, time, and effort you've been putting into making ROHD and its repository better!